↑ 8.08.1Hertig, A. T., and Rock, J. 1941. Two human ova of the pre-villous stage, having an ovulation age of about eleven and twelve days respectively. Carnegie Instn. Wash. Publ. 525, Contrib. Embryol., 29, 127-156.

↑Hertig, A. T., and Rock, J. 1944. On the development of the early human ovum, with special reference to the trophoblast of the previllous stage: a description of a normal and 5 pathologic human ova. Amer. J. Obstet Gynecol, 47, 149-184.